Spin—Rotation Interactions in Polyatomic Molecules

Abstract

Nuclear spins interact with the intramolecular magnetic fields produced by molecular rotation. This interaction broadens and sometimes splits the nuclear-resonance signal observed by molecular-beam techniques. A semiclassical calculation is given for the band shape of such a broadened nuclear-resonance spectrum. One interesting feature of the results is that a logarithmic singularity in the resonance shape may occur if two of the principal components of the spin—rotation tensor differ in sign. The calculated band shapes are compared with several experimental contours, including a spherical-top molecule (CH4), a symmetric-top molecule (C2H6), and an asymmetric rotor (C6H5F). Values of the spin—rotation constants along the principal axes of inertia are thus obtained for these molecules.